The present invention relates to wings, rotor blades, propellers and the like which generate lift or thrust and have a free outboard end at which vortices develop due to the mergence of the fluid flows over the lift-producing surfaces at different pressure and velocity levels. More particularly, the present invention is concerned with wing tips which are designed to alleviate vortices and to improve the overall lift or thrust producing efficiency of the wings.
Vortex alleviation is a well-known problem that has particular importance in large, heavy aircraft with significant span loading. In view of the importance of span loading for such craft, tip vortices generated at slow speeds in takeoffs and landings constitute lethal phenomenon insofar as they affect other aircraft, particularly light aircraft traversing or following in the wake of the heavier aircraft. The hazardous wake region may extend several miles behind larger craft before the effects of vortices are dissipated. The existance of such vortices mandates exceptionally large separation distances between successive aircraft in approach and climb out patterns and, consequently, determines the maximum acceptance rate for aircraft at a particular airport. With the growth of air travel, major airports are forced to build additional runways to keep up with traffic at the maximum acceptance rates. For these reasons, it is desirable to alleviate vortex generation and thereby improve air traffic control and safety.
Additionally, the generation of vortices at wing tips is accompanied by a corresponding reduction in wing efficiency. The flows from above and below the wings normally merge and create the vortex on the upper wing surface inboard of the tip, and as a consequence, the portion of the wing outboard of the vortex origin is washed above and below by the same flow and does not contribute significantly to lift or thrust in the absence of a differential pressure. Also greater induced drag is generated.
The vortex problem is addressed in a number of prior U.S. Patents such as U.S. Pat. Nos. 3,411,738 and 4,108,403. In these patents the configuration of the wing tip is designed to produce certain effects that interfere with the vortex development in the wake of an aircraft. U.S. Pat. Nos. 3,692,259, 3,480,234, 3,841,587 and 4,040,578 all rely upon fluid means to counteract the effect of vortices inherently developed at wing tips. The present invention employs the broad principles of shape refinement and fluid control disclosed in the referenced patents.
It is accordingly a general object of the present invention to alleviate vortex problems in the wake of a lift or thrust producing wing, and at the same time improve wing efficiency.